sourceipk: add class to create source ipks

sourceipk: add class to create source ipks

* Created the sourceipk.bbclass class that can be used to
  package the patched sources and recipe for an application
  into an ipk for installation.
* Allows specification of the installation directory for the
  sources using the SRCIPK_INSTALL_DIR variable.
* Can be enabled per package and controlled through the
  CREATE_SRCIPK variable.
* Creates a README file in the sources directory that
  explains the contents of the package.
* User can specify the package architecture for the source ipk
  using the SRCIPK_PACKAGE_ARCH variable.  The default value is
  "all".
* Using the -L flag to the cp command to copy files pointed to by
  symlinks and not the symlinks themselves.
* Adds source package to list of dynamic packages.

Signed-off-by: Chase Maupin <chase.maupin@ti.com>
Signed-off-by: Koen Kooi <k-kooi@ti.com>